From the module description:

• Try to be less intrusive with OCR-D specific logging conventions to
  make it easier and less surprising to define logging behavior when
  using OCR-D/core as a library
• Change setOverrideLogLevel to only override the log level of the ocrd
  logger and its descendants
• initLogging will set exactly one handler, for the root logger or for the
  ocrd logger.
• Child loggers should propagate to the ancestor logging (default
  behavior of the logging library - no more PropagationShyLogger)
• disableLogging only removes any handlers from the ocrd logger

In short:

• if you want the OCR-D logging conventions, use ocrd_utils.logging.{initLogging,getLogger,disableLogging}.
• if you don't want OCR-D to mess with the root logger, call initLogging(basic_config=False)
• if you want the builtin logging behavior only, call initLogging(builtin_only) which will omit the configuration file lookup
• if you don't want the OCR-D logging conventions, just do not use them. The only side effect of (transitively) importing ocrd_utils.logging now is that all handlers added to the ocrd logger will be removed. I'm open for even removing that but need to think about it some more.

Until now, we implemented --log-level/setOverrideLoglevel by changing the default logger to one that does not propagate and overriding the levels of every logger. Now, we keep the default behavior (all loggers propagate) and only change the level of the ocrd logger. We leave the root logger alone completely.